1. Field of the Invention
This invention is related in general to the field of interferometry and, in particular, to a novel device for measuring the surface roughness of cylinder walls in internal combustion engines.
2. Description of the Related Art
The surface roughness of cylinder walls in internal combustion engines is critical to good performance and durability. When the surface is too smooth, engine oil is thoroughly cleaned away by the recurring scraping action of piston rings over the cylinder walls, thereby greatly reducing lubrication to the parts and correspondingly increasing wear and tear. On the other hand, when the surface is too rough, the rings abut unevenly against the cylinder walls creating nonuniform lubricant distribution, which results in lubricant losses and nonuniform pressure distribution between the abutting surfaces, in turn also producing excessive wear and tear. In the ideal situation, the interior walls of cylinders have a very uniform surface with sufficient microscopic roughness to retain lubricant particles within uniformly-distributed recesses in the wall, such that the surface is never fully depleted of lubricant by the scraping action of the rings. Experience has shown that an average roughness of about 0.2 to 1.5 microns is desirable for standard automobile and truck internal-combustion engines.
In view of this objective, engine manufacturers inspect cylinder walls and measure their surface roughness as normal quality-control steps. The instruments used consist of borescopes, optical devices capable of showing small details of internal features, including imperfections and cracks, and stylus profilometers, mechanical devices for measuring the topography of the cylinder wall, typically with a limited three-dimensional resolution. Boroscopes are not very useful in testing for surface roughness because their resolution is not sufficient to identify problem spots; in addition, they provide a view of the cylinder wall but do not produce a quantified profile of the tested surface. The stylus instruments operate on contact, thereby affecting the tested surface, and have no ability to perform three-dimensional measurements.
Accordingly, there is a need for a better instrument for the purpose of rapidly, reliably and non-destructively measuring the roughness of cylinder walls. This invention is directed at providing a novel instrument and procedure based on non-contact interferometric principles for measuring the surface roughness of cylinder walls.